1. Field of the Invention
The invention relates to a light-emitting element (which is herein used for the same meaning as an LED (light-emitting diode) chip) with a reflective layer and a method of making the same.
2. Related Art
A conventional light-emitting element is known which includes an n-type GaAs substrate, a light reflection layer provided on the n-type GaAs substrate, an n-type Al0.45Ga0.55As cladding layer provided on the light reflection layer, a p-type GaAs active layer provided on the n-type Al0.45Ga0.55As cladding layer, a p-type Al0.45Ga0.55As cladding layer provided on the p-type GaAs active layer and a p-type GaAs cap layer provided on the p-type Al0.45Ga0.55As cladding layer, and in which the light reflection layer has a laminated structure of n-type AlAs/n-type AlxGa1-xAs, the laminated structure is formed in a chirp shape with continuously varied film thickness, and a relation among a variable thickness ratio, the number of laminations and a mix crystal ratio which allows to obtain a predetermined reflection wavelength band and a reflectance is defined. (e.g., see JP-A 5-37017).
Since a light reflection layer in the light-emitting element described in JP-A 5-37017 reflects light proceeded on a semiconductor substrate side by interference of light, it is possible to improve optical output.
However, in the light-emitting element described in JP-A 5-37017, although it is possible to expand a reflection wavelength region by a single light reflection layer, it is difficult to improve light output of the light-emitting element without increasing film thickness of the light reflection layer. In addition, the film thickness of the light reflection layer may be required to be increased in order to improve the light output of the light-emitting element, in such a case however, the production cost may significantly increase, which is an increase in raw materials or growth time, etc., due to an increase in total number of epitaxial layers to be grown.